A standard rotary brush assembly has a flexible, annular and generally cylindrical collar generally centered on an axis and having a predetermined and generally uniform radial thickness, a predetermined inside diameter, and a predetermined axial length. A plurality of arrays of radially projecting bristles angularly equispaced about the collar define a plurality of axially throughgoing and angularly equispaced bristle-free zones. A holder for the brush is comprised of a pair of flange disks each formed with a circular groove of the same diameter as the brush collar, a central screw spindle extending between the disks, and axially projecting tongues radially outside the grooves and spaced to engage in the bristle-free zones of the brush. The axial ends of the collar are fitted in the grooves of the disks with the tongues positioned in the bristle-free zones, and the screw is tightened to clamp the brush in place. This assembly is structurally very stable so that when it is rotated the radial outer ends of the bristles can be counted on to lie on a cylinder centered on the rotation axis of the brush, and the tongues prevent the brush from coming loose even if stressed considerably.
While this arrangement is fairly effective, it is susceptible of improvement.